This invention relates to a process and apparatus for preparing bonded nonwoven fabrics, and is more particularly concerned with improvements in thermal bonding of a web with hot air while conveying the web on a rotating cylindrical roll.
Steam-heated, smooth-faced cylindrical rolls have long been used for drying textile fabrics or paper webs. A recent improvement is to convey the wet web on cylindrical rolls having pervious surfaces and to remove the water by passing hot air through the web. An illustration of such a flow-through dryer is found in Bryand et al. U.S. Pat. No. 3,345,756 dated Oct. 10, 1967.
A flow-through dryer can be adapted to thermally bond webs of thermoplastic filaments. The filaments are heated to the bonding temperature by passing air at a sufficiently high temperature through the web and the pervious surface of the roll into a vacuum zone within the roll. Flat, non-puckered products can be prepared by maintaining the web under high tension, but this results in unacceptably stiff and machine-directional properties. These undesirable properties can be improved by using lower tensions but then the products have a puckered appearance. Puckering appears as ridges or random marble-like bubbles and is aesthically unacceptable for most textile fabric uses.